This invention relates to a bonded structure that provides high adhesion strength through enhanced interfacial diffusion of a bonding material and methods of manufacturing the same.
Bonding of multiple substrates is required to enable three-dimensional integration of chips. Bonding of two substrates can be effected by adhesion between two dielectric materials as in an oxide-to-oxide bonding that fuses silicon dioxide materials from two substrates after bonding, by adhesion between two metallic materials as in a copper-to-copper bonding that employs direct contact between two copper pads and a subsequent grain growth across the original interface between the two copper pads, or by a method employing a combination of the two adhesion mechanisms.
Through-substrate-via (TSV) structures, formed after multiple substrates are bonded and optionally thinned, provide electrical connection across the multiple substrates in a bonded structure. A TSV structure includes a conductive material such as copper, which diffuses rapidly in the plane of the bonding interface between substrates because microscopic irregularities and cavities are present at the interface. Diffusion of the conductive material from a TSV structure can cause electrical shorts and reliability problems in the bonded structure.
An interface between diffusion resistant materials, such as silicon nitride, across bonded substrates can be employed to reduce later diffusion of conductive material from TSV structures. In this case, the diffusion resistant materials retard lateral diffusion of the conductive material from the TSV structures along the interface between two bonded substrates, thereby preventing electrical shorts.
The adhesion strength between the two substrates is mostly provided by the metal-to-metal contact between the metal pads that are embedded in the diffusion resistant materials. To provide sufficient adhesion strength between the two substrates in this type of structure, atomic diffusion of the bonding material to mix metal atoms needs to be effected. To provide sufficient atomic diffusion of metallic materials, a high temperature anneal for an extended time is needed, for example, in an anneal at a temperature about 500° C. for many hours. Such a prolonged anneal at an elevated temperature adversely affects the performance and reliability of semiconductor devices in the bonded substrate.